Implement hold-down device



Oct. 13, Q W. MOTT ET AL l IMPLEMENT HOLD-DOWNDEVICE Filed March 26,v 1940 4 Sheets-Sheet l Filed March 26, 1940 4 Sheets-Sheet 2 {fra/rions (fami Zz/O/ 275/15,

Oct. 13, 1942. C- W- MTT ET AL- 2,298,539

IMPLEMENT HOLD -DOWN DEVI CE Filed March 26, 1940 4 Sheets-Sheet 3 N O Y mfamwMf/oso m www Oct' 13 1942 c. v v. MOTT ET AL IMPLEMENT HOLD-DOWN DEVICE 4 sheets-sheet 4 Filed Maron 2e, 1940 u Q n k NN Y Nm; ,wh .NN .bb 9% Patented Oct. 13, 1942 UNITED `snrrEs PATENT o-FricE ments for use with ground-workingltillage implements, such as cultivators, which are directly connected to a tractor for movement to and from its ground-working position andadapted to be moved, at least from its ground-workingposition, by means of a power lift deviceassociated with the tractor.

It is an object of the invention to have a 'biasing means associated withthe power lift Vdevice ,Y

which may be of a single acting type whereby the spring v4will tend to VCollapse the device when the rigs are lowered to ground-,working position whereby a double acting effect willbe given tothe power lift arrangement.

It is another object of this inventionto provide such a biasing Varrangement Vadapted Yfor holding the implement in the ground whereby, upon operation of the power lift, or lifting means, such spring means will automatically rbe ineffective upon operation of the lift device, or, in other words, will not Work materially against the lifting means when the same is operatedto lift the cultivator rigs.

It is another object ofthe invention to sc arrange the spring device with reference to the i connections between the power lift device and the cultivator rig that the entire arrangement is simplifiedand at the same time permits the arrangement to be particularly radapted for manual adjustment to regulate the working depth of the cultivator rigs.

According to the present invention,there h as been provided a spring arrangement which is adapted to be associated with a single acting hy- ...c

draulic lift device wherein, upon operation of= the hydraulic lift device to lift the implement, the spring means will yield or vary to render itself relatively ineffective upon operation of theA hydraulic cylinder. Upon release of the lluidfrom the hydraulic cylinder, the spring means will serve to force the uid out of the cylinder lvfor return to its reservoir and at the same time will tend to exert force upon the implement to cause it to enter into the ground. With a cultivator rig, there is always the tendency for the rig-to leave the ground and it is toY lessen this tendency that such cultivator rigs are connected to the tractor by means of parallel link arrangements.

This hold-down spring of the present invention is so arranged with respect to the cultivator rig that a force will be continually exerted upon the rig to maintain the same in the ground or toen- `force the cultivator rigs into the ground where the soil is of such hardness that additional .weight I is.necessarylto,gety the rigsinto theground and tomaintain-thm therein. VIhus, it maybe said that the spring, arrangement of thepresent invention willy inreiectsupplymore weightto the rigs .for the maintenancefof the same in the ground. Because undesirable to lift against the-action olfftheo-spring'the spring is so arranged that littlegadditional effort is required to lift the implement with Tthe spring connected thereto :for rnormally .l'iol'ding fthe same inv its ground-.working position.`

Forotherobyjectsand for a better understanding ofthe invention, reference may be had-to the A.followingdetailed description taken in. connection with the 'accompanying drawings, in which:

--Figure l is anelevatonal view of va .tractor showing one form of the vspring arrangement associated with afhyslraulic cylinder;

EigurgeZ isa .sectionaltand detail view of the spring-and `illustrating.its connections with the arraeemeni Figure J3 is.a plan view ofthe tractor shown in Figure 1. and-:showing identical arrangements at opposite sfidesof the tractor for lifting respectively those implements at that particular side ,ofthetracton Figurel isa view similar to `Figure 1 of va tractor. in. elevation yand illustrating another form of` the Ispringv arrangement;

Figure 5`is':v avievv` showing the spring arrangement ofV Figure-4in its `extended position;

Figure.6 is .still another form of the invention showinga-tractorin elevationand with' the implementsin their ground-working position; and,

-Figure 7 isaview showing the spring arrangement. ofFigure-and showing the same in its .extendedposition AReferringnovv tothe-.form of invention shown in;Fi g ures-1, 2,. and ..3,= there is shown a tractor I0 lhavinga forwardportion Hand a rear portion I2. VA'The rearportion-IAZ includes. a transmission and. diierential-housing-I .and a transverse axle housing I4 extending laterally from each side of Vthe housing- I 3.

vO ntl'ie forward portion II,-there.may be connected a` transve rsely` extending tool-,supporting bar I5'adapted.to s upport the brackets I6 atany position transversely therealong and to which there is connected ,foreach-of the cultivator rigs upper and lower parallel links I'I'and I8. To the `rearendzof theseparallel linksisconnected a `cultivator righI 8 having .cultivator shovels 20. On .a pair of Vtliebrackets I.6,.there maybe pivoted .a hairpinlever element 2| adapted for movement in a fore and aft direction with respect to the tractor. To the upper end of the hairpin lever element 2l, there may be connected a lift pipe 22 which extends rearwardly along the side of the tractor for connection with a hydraulic cylinder lift device 23, which may be supported on a bracket structure 24 carried by the laterally extending axle housing I4 at the rear portion of the tractor. Briefly, this hydraulic cylinder device 23 is adjustably connected to the bracket structure 24 as indicated by the manual adjusting means 25 accessible to the operators station 26 on the rear portion of the tractor.

The hydraulic cylinder device may be of the usual construction and is of a single acting type whereby fluid power is exerted only to one side of the piston element. This iiuid power may be obtained from a reservoir and pump arrangement 21 adapted to receive power from the transmission and differential housing I3. This pump and reservoir housing may be controlled by a control rod 28 also accessible to the operators station 26. By a pull upon the control rod 28, fluid is caused to pass through the fluid communications 29 and 30 to the rearward end of the cylinder device to force the piston forwardly and also to force the piston rod 3I associated therewith forwardly for abutting engagement with a stop element 32 within the pipe 22. See Figure 2.

The forward end of the lift pipe 22 has a laterally extending flange 33 through which passes pressure spring rods 34 connected at 35 to the cultivator rig I9. When forward movement is given to the lift pipe 22 the forward end thereof is caused to move about an arc because of its connection with the lever 2| and, when the plate 33 abuts with a set collar 36 on the lift rod 34,v

the rig I9 will be lifted from its ground-working position to take the position shown in Figure 1. Each of the pressure rods 34 carry a pressure spring 31, which abuts at its lower end a set collar 38. When the rig I9 is in its groundworking position, there is a continual pressure exerted upon the rig by virtue of these pressure springs 31 wherein the upper end of the same reacts against the plate 33 on the lift pipe 22. If some means is not provided to hold the lift pipe 22 xed with relation to the piston rod 3I, the action of these springs 31 will not be effective. Thus, some means is necessary to maintain the lift pipe 22 substantially fixed with reference to the piston rod 3| of the cylinder device 23.

For accomplishing this, there has been provided byy the present invention a biasing spring arrangement which has su'icient strength to hold the lift pipe 22 substantially rigid when the implements are in their ground-working position. This spring arrangement may be identified as a master hold-down pressure spring or biasing device. This device provides means for holding the single-acting fluid cylinder device collapsed to thereby render the hold-down pressure spring means operative and effective when the implement is in its ground-working position. In the form shown in these Figures l, 2, 3, this holddown spring may take the form of a spring which will buckle when great force is applied to either end of the same. However, the spring must be of such dimension and so arranged as to accomplish the -function desired of it.

Thus, according to this form, there is shown a buckling spring 4I having threaded into its ends respectively the pivot elements 42 and 43. The pivot element 42 may be pivotally connected to a bracket 44 secured as by welding to the rear end of the lift pipe 22, as indicated at 45. The pivot element 43 is pivoted to a bracket 46 which is secured, as by welding indicated at 41, to a rearwardly extending link element 48 which is connected to the tractor by connection to the rear end of the Cylinder device 23, as at 49, which is in turn connected to the tractor through the bracket structure 24.

This buckling spring 4I will normally tend to maintain its straightened position shown in Figure 2, but, when acted upon by the cylinder device 23 acting through the piston rod 3l to move the lift pipe 22 forwardly for effecting lifting of the implement, it will suddenly yield thereby diminishing the force acting against the action of the cylinder device. In a sense this type of spring acts as a toggle and suddenly gives way to render the same substantially ineffective upon applying power to lift the implement. However, when the spring is in its normal position, the force is suiciently great to overcome any action of the implements working on pressure springs 31. Should the cultivator shovels meet a sufficient obstruction whereupon the pressure springs 31 might be completely compressed, the master hold-down spring 4I would yield suddenly and thereby prevent any breakage of parts. The bracket 46, to which the pivot element 43 is connected, remains stationary and the pipe 22 may slide through the same. The pivot elements 42 and 43'have threaded portions 42 and 43', respectively, by which the ends of the spring 4I may be connected so that the spring may be held equally as well in tension as in compression.

Referring now to the forms of the invention shown in Figures 5 to '1, similar numerals to those used above will be used only in so far as they apply to the tractor. A new set of numerals will be used for the cylinder device, cultivator, and connection of both of these parts to the tractor and to each other. In these gures, there is shown a slightly different form of tractor but having generally a similar forward portion I I and a similar rearward portion I2. The pump and reservoir housing 21 is, however, somewhat diierently connected to the transmission and differential housing I3. The fluid communication 29 is partly within the housing I3 and is vconducted from the same through an opening 50 for connection to a cylinder device 5I. This cylinder device has a rearwardly extending sleeve 52 rigidly projected from the same for sliding connection with a supporting sleeve 53 pivotally connected at its rear end, as indicated at 54, to an adjusting mechanism 55 which is in turn carried on a bracket structure 5G supported by the transverse axle housing I4. Extending through the projected sleeve 52 is the piston rod 51. This piston rod 51 abuttingly engages with a locking element 58 connected with a detent 59 of the adjusting mechanism 55. As the rear end of the piston rod 51 abuts this locking element 58, the lock element and the detent 59 will be held rigidly and it will be impossible for the adjusting mechanism 55 to be adjusted at this time. In order for the piston rod 51 to extend through the rear end of the sleeve 54 for abutting engagement with the lock element 58, the sleeve 53y has connected at its rearward end, as by welding,v along its sides straps 60 for the connection of the sleeve 53v to the adjusting mechanism 55 at 54. By this arrangement, the adjusting mechanism is automatically made inoperable when fluidpressure is supplied to the hydraulic device 5I.

Connected to the forwardportionof thetractor there is a transversely projected-tool-supporting-bar 6|, to which Vsupportingqmeans GZ-'may be-connected, for the attachmentof upper and lower parallel links 63 and 64|, tothe lowerend of which is connected a cult-ivator-rigl'65 having the cultivator shovels 66. On `the supporting means 62 is connected Va-fore and aft movable lifting lever element 6l. On-the'bracket structure VA56 at the rear of the tractor'there-is-likewise pivoted a similar pivoted lever element l68,

as indicated at 69, and extendingbetween these two-lever elements 6`| and 68 and pivotally` connected therewith respectively at their freeends, as at-| and is a liftingrpipe1'ig2. The-lifting 'levers 61 and 68 and the lifting'pipe 'l2 provide a structure which is adapted to move fore and aft y:and to which a cultivating rig is attached for effecting lifting of the same. In thevpresent instance, the lift pipe YI2 has a laterally extending flange element 73 through which the lift rods 'M may normally slide when the cultivator rig is in its ground-working position, but soadapted that, vwhen the lift pipe is moved forwardly to pivot the pivot levers 61 and 68,.the plate'13will engage with a set collar 'l5 to effect lifting ofthe cultivator rig. When in the ground-working position, the cultivator shovels 66maintain their ground-working position by the usual pressure springs 'i6 reacting between the flanges 13 .and a set collar on the pressure rod VHL Intermediately of the ends of the liftpipe '12, there is connected a bracket 'i8 by .fwhichthe cylinder device 5| effects movement of thelift pipe forwardlyto effect the lifting of the cultivatorrig. The cylinder device 5| is connected to the bracket 18, as indicated at 19, and the `same is at least in part supported therefrom.

.Up totln's point of the description, theparts Vshownin all of the Figures 4 to 7, inclusive, are

substantially the same. The dilerencebetween -the Figures 4 and 5 and Figures 6 and 7.remain only in the. elements used for theattachment. of thebiasing spring. Reference .should now behad to the form of the invention shown in Figures 4 and.5. In this form of the invention, there is pivoted to the forward end of the sleeve. 53 a lever element 81| of substantially triangular shape, as atil, and preferablyincludes two spacedplates. Vertically removed from the point ofconnection 8|, there are points of connection 82 andl 83 thereon. Connected between the point ofcon- `nection B2, which is intermediate ,thepoints of connection 8| and 83 is a tension spring 8,4. The springr84 is preferably connected at 82-through a link 85 in order to prevent interference of 4the spring with the lever element 80 upon the same being rotated from one position to another `position. The other end of the spring 84 is threaded to a retaining element 86 which is adjustable with reference to a flange 81 rigid with the rear end of the pipe sleeve 53. This adjustment is effected by an adjusting bolt 88 threaded into the element 85.

The point of connection 83 of the lever 88 has connected to the same a link 89 which in turn is connected at 19 to the bracket 'I8 on the lifting pipe 72. When the power lift device 5| operates, the link 89 will move forward with the same to effect clockwise pivoting of the lever element 80 about its point of connection 8| with the sleeve 53 to take a position as shown in Figure5. Normally, however, the spring 84 is acting on thelever element 80 at 82 to prevent forward movement of the'lift pipe "|-2 and thereby vto re- 75 tainthe ycultivator.shovels 66 in their groundworking position. The force `with which this spring-84 -acts will Adepend upon the setting of the adjustingfbolt 88. Adjustment of theV bolt 88 ma-yfbemade to give the spring any-desired initial tension.

Whenrthevcylinder -5| and the pipe rod 'I2 connected thereto moves forwardly, the piston rod 5`| will react against the adjusting mechanism 55 andthe lever element 80 will be rotated in aclockwise direction. The spring 84 will naturally tend to resist movement of the cylinder device and, as the lever element rotates, the spring will be acting -with greater force and becomes effective,1but the percentage effectiveness of the force of the spring reacting against the lift device will=be diminished by virtue of the fact that the effective arm between the link 89 and the pivot point` 8| lengthens and the effective ann between the connection element and the pivot point 8| shortens. It should thus be seen that by this system of a lever element the resultant force of the spring'84, which would tend to prevent operation of the hydraulic device, will not reach a substantial amount andfthat it is, by arrangement of a lever such as shown, rendered less effective. While it is true that, upon increase in the length of a spring, the force required to tension the same has a straight-line function with the length as the same has been expanded and that the spring will build up a large total force, but it should be apparent that this increased force is compensated for by a changing -of the lever arms so that the resultant force act- :ing Vagainst the operation of the cylinder device .5| is not materially greater than the original vvacting `when the implement is in its ground- `working position. It should thus be seen that in this form ofv theinvention there'has likewise lbeen -provided a spring arrangement adapted normally to hold the Acultivator Vrigs in their Vground-working position, which spring arrangement'automaticallyupon operation of theliftdevrvice becomes relatively ineffective, so as not to toogreatly hinder the operation of the power lift device.

Referring now to the form-of invention shown in Figures 6 and '7, there is shown a similar arrangement of a spring device, but one wherein the pivot element 86 may be connected at a p oint ,removed lfrom the forward end 0f the sleeve 53. BysllCh anarrangement, it is possible somewhat togsimplify the construction and at the same time to tend to eliminate as faras possible side force acting' intermediate the ends of the arrangement to causea side thrust upon the sleeve 53, so that easy sliding operation of the same over the projecting sleeve 52 of the hydralulic device 5| is had. `It has been found that, by having the pivot element 80 connected, as shown in Figures 6 and 7, smoother operation of the device will result. It is, therefore, to be regarded that the forms shown in Figures 6 and '7 are apreferred form ofthe invention.

In this form of the invention, thelinkelement 9D corresponding to the link element'e, has an offset portion 9| adapted to receive the adjusting bolt 92, to which is adjustably connected the connectingv element 93 'for the connection of a spring 94. The other end of the spring S4 is connected through a connecting element 95 to an intermediate-point of connection 96 of a pivot element 9'! -corresponding to the pivot element 83 of the form shown in-Figures 4 and-5. 'I'he pivotal element Slis-vin tu-rn pivoted'at-'S to the sleeve 53, -but'at a point substantially removed from the forward end of the sleeve 53. The link 9D is similarly connected to the pivot element 81, as indicated at 99, and is connected at to the element 18 of the lift pipe 12. By this arrangement, the spring 94 acts very closely along the central axis of the sleeve, so that minimum side thrust is exerted which would in any way tend to cause rubbing of the sleeves 52 and 53. As the cylinder device is actuated, the arrangement will finally assume a position shown in Figure 7, the pivot element 91 having been pulled by means of the link 90 about the pivot point 98 on the sleeve 53. Since the point of connection 96 of the spring with the lever element 91 is intermediate the points 98 and 99, a changing leverage effect may be given to the same, so that the resultant force acting against the power lift will not be greatly increased beyond the initial setting of the spring by the adjusting means 92.

In Figure 4 is shown the implement or cultivator rig positioned immediatelylprior to the,

same being forced into the ground. Assuming that the ground is hard, it should be apparent that additional weight is necessary for the cultivator rigs to be forced into the ground. By means of the arrangements of the present invention, this additional weight is supplied. The spring arrangements enable the power lifting means to have somewhat the effect of a double acting arrangement whereby the piston is retained when the uid has left the device. With the piston being so retained, the lift pipe 12 will be given a definite retracted position properly to locate the flange 13, depending upon the depth adjustment of the adjusting mechanism 55. With the liftrod 12 and its flange 13 given a definite position, the pressure rod spring 16 will thereby be given something against which it may react, and, if said spring is properly set,

it is very likely that the cultivator shovels 66 will be forced into the ground thereby to assume the cultivating position shown in Figure 6. Upon operation of the power lift device, the flange 13 will Contact with the stop collar 15 to lift the cultivating rig to the position shown in dotted lines in Figure 6, and at the same time to cause the spring arrangement to take the position shown in Figure '1.

It should be apparent that, by the three forms of the invention disclosed, a spring means for holding cultivating rigs in the ground has been provided and that such an arrangement has been so devised that the operation of the lifting device is not greatly impeded.

While various changes may be made in the details of the arrangement, it shall be understood that such changes shall be within the spirit and scope of the present invention as defined in the appended claims.

What is claimed is:

1. In combination, a tractor, an implement mounted on the tractor for vertical movement to and from its ground-working position, means for lifting the implement including a singleacting hydraulic cylinder lift device adapted to react against the tractor and having a movable part, and a part relatively movable with respect to the movable part of the cylinder lift device, biasing spring means, and means for connecting said biasing spring means between said lastmentioned part and the tractor to hold both of said parts in spring biased and collapsed relationship when said device is freed of hydraulic pressure and the implement is in its groundworking position.

2. In combination, a tractor, an implement mounted on the tractor for vertical movement to and from its ground-working position, a power lift device for moving the implement from its ground-Working position, and spring means adapted to be buckled by the power lift device upon operation of the same but tending to straighten upon release of the power lift to resiliently force and retain said implement in its ground-working position.

3. In combination, a tractor, an implement mounted on the tractor for vertical movement to and from its ground-working position, a single-acting hydraulic power lift device having a movable part, means for abuttingly connecting the movable part to the implement, a buckling spring connected between said connecting means and the tractor to normally hold the implement in its ground-working position and at the same time to hold the hydraulic device collapsed, and said spring means being so arranged as to buckle when the implement strikes an obstruction and upon operation of the power lift device.

4. In combination, a tractor having forward and rearward portions, an implement mounted on the forward portion of the tractor for vertical movement, a pivoted lifting lever at the forward portion of the tractor, a bracket structure at the rear of the tractor, a single-acting hydraulic cylinder device adjustably connected at one end to the bracket structure and having a movable piston rod, a fore and aft movable lift pipe connected to the lever and to the implement, said pipe telescopically arranged with respect to said piston rod which abuttingly engages with the pipe internally thereof to effect lifting of the implement, and spring means connected between said pipe and the tractor through the bracket structure and tending to maintain the cylinder collapsed whereby bodily adjustment of the cylinder device will eiect adjustment of the implement, and said spring means being made substantially ineffective upon operation of the cylinder device to effect the lifting of the implement.

5. In combination, a tractor, an implement connected to the tractor for vertical movement to and from its ground-working position, power means including a movable part, means for connecting the power means to the implement including a part adapted to be engaged by said movable part of the power means, and spring means adapted to normally hold said movable part in engagement with said part adapted to be engaged thereby when the implement is in its ground-working position, said spring means being so connected and arranged between said parts as to be made substantially ineffective between the two parts after operation of the power Vmeans through a small amount of its movement.

6. In combination, a tractor, an implement connected to the tractor for vertical movement t0 and from its ground-working position, a single-acting hydraulic cylinder device connected to the tractor and having a piston rod, means for connecting the piston rod to the implement to move-the same including a pipe telescopically arranged about said piston rod and adapted to be operatively engaged by the same internally thereof, a buckling spring pivotally connected at one end thereof to the pipe and at its other end thereof to the tractor, said spring being buckled by the cylinder device upon operation of the same to move the implement but tending to straighten upon release of fluid from the cylinder device to collapse the same and to resiliently retain the implement in its ground-working position.

7. In combination, a tractor, an implement connected to the tractor for vertical movement to and from its ground-working position, a power lift device for moving the implement and having relatively movable parts, one of said parts being connected to react against the tractor and the other being connected to the implement, and biasing means connected around said relatively movable parts to normally hold the parts collapsed with respect to each other, said biasing means including a lever element pivoted relatively to and between said parts, the pivot connection to one of the parts being removed from the pivot connection to the other of said parts, and a biasing spring connected between one of the parts and the lever element, the point of connection of the spring with the lever element being intermediate the two pivot connections of the lever with the respective parts, said lever element being so shaped and arranged with respect to said parts that, upon operation of the power lift device, the lever is forced to move about at least one of itspivot connections, whereby irrespective of the placing of increased energy into the spring the resultant effect acting between the parts is minimized.

8. In combination, a tractor, an implement connected to the tractor for vertical movement to and from its ground-working position, a singleacting power lift device connected to the implement to lift the same and including relatively movable parts, one of the parts adapted to react against the tractor, biasing means for holding said parts against relative movement comprising a lever element pivotally associated with relation to one of said parts, a link pivotally connected to the lever element and to the other of said parts whereby, upon forcible separation of said parts, the lever element will be rotated, and spring means connected to the tractor and to the lever at a point between the connection of the link thereto and its point of pivotal association with one of the parts, whereby, when the lift device is operated, the resultant effectiveness of the spring between the parts will be prevented from greatly increasing.

9. In combination, a tractor, an implement connected to the tractor for vertical movement to and from its ground-working position, a singleacting power lift device connected to the implement to lift the same and including relatively movable parts, one of the parts adapted to react against the tractor, biasing means for holding said parts against relative movement comprising a lever element pivotally associated with relation to one of said parts, a link pivotally connected to the lever element and to the other of said parts whereby, upon forcible separation of said parts, the lever element will be rotated, spring means connected to the tractor and to the lever at a point between the connection of the link thereto and its point of pivotal association with one of the parts whereby, when the lift device is operated, the resultant effectiveness of the spring between the parts will be prevented from greatly increasing, and means for adjusting the spring means to vary the force tending to hold the parts together.

li). In combination, a tractor, an implement connected to the tractor for vertical movement to and from its ground-working position, a single-acting power lift device connected to the implement to lift the same and including relatively movable parts, one of the parts adapted to react against the tractor, biasing means for holding said parts against relative movement comprising a lever element pivotally associated with relation to one of said parts, a link pivotally connected to the lever element and to the other of said parts whereby, upon forcible separation of said parts, the lever element will be rotated, and spring means connected to the link and to the lever at a point between the connection of the link thereto and its point of pivotal association with one of its parts, whereby, when the lift device is operated, the resultant effectiveness of the spring between the parts will be prevented from greatly increasing.

11. In combination, a tractor, an implement connected to the tractor for vertical movement to and from its ground-workingposition, a single-acting power lift device connected to the implement to lift the same and including relatively movable parts, one of the parts adapted to react against the tractor, biasing means for holding said parts against relative movement comprising a lever element pivotally associated with relation to one of said parts, a link pivotally connected to the lever element and to the other of said parts whereby, upon forcible separation of said parts, the lever element will be rotated, spring means connected to the link and to the lever at a point between the connection of the link thereto and its point of pivotal association with one of its parts, whereby, when the lift device is operated, the resultant eifectiveness of the spring between the parts will be prevented from greatly increasing, and means for adjusting the spring means at its point of connection with the link to vary the force tending to hold the parts together.

12. In combination, a tractor, an implement connected to the tractor for vertical movement to and from its ground-working position, a single-acting power lift device connected to the implemenfl to lift the same and including relatively movable parts, one of the parts adapted to react against the tractor, biasing means for holding said parts against relative movement comprising a lever element pivotally associated with relation to one of said parts, a link pivotally connected to the lever element and to the other of said parts whereby, upon forcible separation of said parts, the lever element will be rotated, said link having an oiset portion, spring means connected at one end to the lever element at a point between the connection of the link thereto and its point of pivotal association with one of the parts, and means for adjustably connecting the other end of the spring means to the oifset portion of said link, whereby, when the lift device is operated, the resultant effectiveness of the spring between the parts will be prevented from greatly increasing.

CARL W. MOTT. JAMES MORKOSKI.' 

